Various floating particle detection devices for detecting scattered light generated when a space in which floating microscopic particulate matter (hereinafter referred to as ‘floating particles’), such as pollen and dust, is present is irradiated with light, and performing detection or identification of a quantity of the floating particles, size of the floating particle, or a type of the floating particle have been proposed.
For example, patent document 1 describes a pollen sensor that distinguishes between pollen and soil dust and that includes: a light emitting means for emitting a laser beam in a horizontal direction toward a detection-target region; a first light receiving means disposed in a position at an angle of 60° obliquely upward from the center position of the detection-target region with reference to the horizontal direction; and a second light receiving means disposed in a position at an angle of 60° obliquely downward from the center position of the detection-target region with reference to the horizontal direction.
Patent document 2 describes a particle sensor that includes a semiconductor laser and a light receiving element and that converts a laser beam radiated from the semiconductor laser to a substantially parallel light flux with a lens, detects scattered light generated when a floating particle is irradiated with the laser beam of the parallel light flux with the light receiving element, and thus performs detection of a quantity of the floating particles and identification of size of the floating particle.